1. Field of the Invention
The present invention relates to a semiconductor integrated circuit apparatus, and more particularly to an apparatus having, integrated on a semiconductor substrate, an active element such as a transistor and a passive element such as a capacitor, the apparatus being used for a signal transmitter of a wireless communication device such as a cellular phone using a radio frequency band.
2. Description of the Background Art
In general, in order to obtain a high output, a semiconductor integrated circuit apparatus for use in a radio frequency signal power amplifier is configured such that a plurality of transistors (for example, heterojunction bipolar transistor) having a superior radio frequency characteristic are connected in parallel with each other so as to combine outputs of the respective transistors. This configuration is disclosed in, for example, U.S. Pat. No. 5,608,353, U.S. Pat. No. 5,629,648, and Japanese Laid-Open Patent Publication No. 2001-196865. FIG. 6 is a diagram illustrating an example of a configuration of a conventional semiconductor integrated circuit apparatus 100 so configured. A semiconductor integrated circuit apparatus 100 shown in FIG. 6 is configured such that a plurality of cell circuits (circuits each enclosed by dotted lines in FIG. 6) each including a transistor 101, a capacitor 102 and a resistor 103 are connected in parallel with each other.
In FIG. 6, a DC bias supplied from a bias circuit (not shown) is supplied to a base B of each transistor 101 via each resistor 103. On the other hand, a radio frequency signal which is an AC signal is inputted to the base B of each transistor 101 via each capacitor 102. Thus, a DC bias and a radio frequency signal are inputted to the base B of the transistor 101 via different routes for the following reasons.
The transistor 101 generates a heat due to a current density of an AC current being increased during a high output operation. Such heat generation is not uniform among all the transistors 101 due to characteristic variations among the transistors 101 and the like. Therefore, a certain transistor 101 of a high temperature exhibits a thermal runaway due to a high heating value during operation, which may cause an element destruction due to an increased base current. Therefore, in order to suppress the thermal runaway, a resistor (base ballast resistor) 103 is serially connected to the base B of each transistor 101 so as to reduce base bias current supplied from the bias circuit when a base voltage is increased in the transistor 101. However, the resistor 103 causes a power gain reduction for a radio frequency signal. Therefore, a radio frequency signal is inputted to the base B of each transistor 101 via the capacitor 102.
However, in the conventional semiconductor integrated circuit apparatus 100 shown in FIG. 6 of the aforementioned configuration, a portion of radio frequency signals supplied to the base B of the transistor 101 via the capacitor 102 escapes into (leaks into) a bias circuit via the resistor 103. Therefore, there is a problem that the escape of the radio frequency signal causes an interference between a DC bias and a radio frequency signal, thereby generating a noise. That is, there is, for example, a problem that when a nose is generated from a power amplifier of a signal transmitter in a wireless communication device, the noise is detected in a signal receiver, which represents a quality degradation of a received signal.